1. Field of the Invention
The present invention relates generally to systems using dissolved air flotation as a means for purification of liquids. More particularly, the present invention relates to discharge valves or nozzles for dissolved air flotation treatment units. Even more specifically, the present invention relates to a self-cleaning valve for discharge of a stream into a vessel of water to be treated, wherein the stream is pressurized and either saturated or supersaturated with oxygen or air and wherein the water to be treated is maintained at a lower pressure.
2. Description of Related Art
Various processes referred to as dissolved air flotation (DAF) systems have been developed and employed to clean or partially clean contaminated liquids by utilizing dissolved gases. The treatment liquid usually contains dissolved oxygen, at a saturated or supersaturated level. See, for example, U.S. Pat. No. 4,956,080 issued to MICROLIFT SYSTEMS, INCORPORATED of Sturgeon Bay, Wis. on Sep. 11, 1990.
In such processes, the treatment liquid frequently is maintained at an elevated pressure and the effluent or other material being treated is kept at a reduced or ambient pressure. The pressurized treatment liquid is introduced into the effluent, thereby allowing the treatment liquid to depressurize. During pressure reduction, bubbles of air or gas are formed as the gas is released from solution. The bubbles float to the top of the treated liquid, carrying particles and other various contaminants. To control the rate at which the treatment flows into the low pressure effluent, a discharge head, discharge valve, pressure reduction valve having a restriction is used.
A common problem encountered in DAF systems is that the treatment fluid is (in the case of fully pressurized or full forward flow systems) raw influent or, at least in part, recycled or partially cleaned effluent. This liquid may still contain some particulate contaminants. Thus, the discharge heads or valve mechanisms may become clogged with these contaminants or other particulate matter. Cleaning can only be accomplished by shutting down the entire DAF system to access the clogged mechanism. A valve or discharge head capable of self-cleaning by periodic purging would reduce system shutdowns, and therefore would represent a significant advancement in the art.
A second and common problem encountered is the normally fixed and manually only adjustable nature of existing discharge heads, discharge valves, or pressure reduction valves used for this purpose. Thus, as the heads or valves become clogged with particulate, they also become restricted and the flow or liquid throughput becomes less. Readjustment of flow (further opening of the valve) becomes a manual operation requiring periodic human intervention and adjustment. A discharge head or valve capable of remote adjustment, and even automatic adjustment by remote control, would reduce maintenance time. Additionally, a remote controlled piston-operated head or valve allows for adjustment of various flows without mechanical human adjustment with wrenches or the like during initial system set-up or subsequent system rebalancing required in many cases because of varying system flow requirements.